


Blowing Off Steam

by sithlady



Category: The Mortal Instruments Series - Cassandra Clare
Genre: Experimentation, Femslash, Multi, Threesome, isaclace?
Language: English
Status: In-Progress
Published: 2017-04-22
Updated: 2017-04-22
Packaged: 2018-10-22 19:06:29
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 4,382
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/10703223
Author URL: https://archiveofourown.org/users/sithlady/pseuds/sithlady
Summary: Isabelle is in a funk following Simon's rejection at the Academy.What happens when Clary invites Isabelle to share her golden god of a boyfriend...?





	1. Chapter 1

**Author's Note:**

> So this happened. It was an accident but I'm not taking it back. 
> 
> Curioser and curioser...
> 
> (I haven't edited this thoroughly- I have a lot going on today but I wanted to get this idea out of my brain so I can explore where it'll go from here. Ignore any mistakes; I'll look it over another day!)

Clary was acutely aware of a bead of sweat that ran down the hollow of her back as she ducked a punch, sliding her leg out from under her to knock the man she fought off his feet. To any normal human, this fight would be unfairly balanced: one tiny redhead against a tall, golden man. But Clary wasn't a normal human, she was a shadowhunter. 

Jace lost his footing, tumbling into a roll as he fell towards the floor. Just as suddenly, he was on his feet again, retreating a step to brace himself. He held back slightly and it only seemed to piss Clary off more. Not that she was really mad, but any good fight requires a certain amount of fury. 

“Don't treat me like a child,” Clary spat, grabbing her training sword off the ground where it was knocked out of her hands a moment earlier. Her long curls fell into her face as she chided Jace who took the momentary visibility issue as an invitation: he rounded on Clary, his sword raised high. 

Their swords hit with a clang and Clary felt the blow radiate through her arms, the energy rippling through her, only inspiring more determination. She gritted her teeth and pressed her efforts forward, bowing beneath Jace’s arm as he swerved his blade away from her own. Clary pressed her back against the wall, using the solid plane for support as she jumped up, kicking her partner square in the chest with both feet. Jace stumbled, sucking in a breath as he steadied himself. For the millionth time, he marveled at the power Clary held in such a small body. She was not only short but also petite, and anybody crossing her on the street would never guess she could hold her own against a man with the muscles and height on her that Jace had. But they didn't know Clary. What she lacked in strength, she made up in her swift agility and clever tactics. 

Jace and Clary circled each other, weapons drawn and faces determined. It was only when Clary reached for her stele that Jace pounced, knocking the sword from her hands once again, pinning her against the floor. “Yield,” he said, his breathing hardly affected by their fight. 

“No,” Clary hissed as she brought the stele to Jace’s tanned skin. She always wondered how he stayed so tan, as he certainly wasn't the sunbathing type, nor did any of them spend much time lounging outside. Much to Clary’s relief, Jace was so caught up in his perceived victory that he didn't feel the small sting of the stele before a sense of peace passed over him. _Calm anger._

“Clary,” Jace breathed, suddenly assessing their position with less aggressive eyes. The redhead grinned as her green eyes found his, and when Jace brought his lips hungrily to hers, Clary used all her strength to push him off of her. Reaching into her boot, she expertly procured a short blade and was on top of Jace, the knife at his throat. “ _You_ yield,” Clary hissed, her face intoxicatingly close to her boyfriend’s. 

“How did you…?” Jace questioned, lust battling with curiosity. As a response, Clary sat up, grabbing Jace’s arm and holding it up for him to see. 

“You're too easy to distract, Jace,” Clary purred, the knife still held at his throat. She sat flush against his body and felt the hard length of him under her ass; it was all she could do to suppress a groan. “I hope you're not always so easy to manipulate when you've got a girl under you.”

Jace grabbed onto Clary’s hips, grinding them down against him. Clary did groan then, and, as if catching herself, she pressed the knife harder against the bronzed shadowhunter’s threat. The skin beneath the knife turned white and Clary sucked in a breath at the sight. Before she could think, her lips were beside the blade, tasting the salt on his skin. He smelled as he always did, of pepper and leather and the intoxicating hint of sweat which made Clary moan against his throat. 

“You're so fucking hot,” Jace groaned, his hands slipping under the waist of the redhead’s pants to grab her ass, his nails digging into her flesh. Clary whimpered, letting the knife fall onto the training mat next to them as she sat up, gasping. A single bead of blood pearled to the surface on Jace’s neck and, before she could think, Clary’s tongue was on it, tasting the sweet iron tang of her boyfriend’s blood. When she pulled back to look at Jace, her eyes were dark and ravenous. Jace saw a smudge of his blood against Clary’s open bottom lip and groaned, bending up to lick it off of her. Their lips came together desperately, tasting of blood and sweat and unadulterated need that left them gasping. 

“And yet, it always ends like this,” came a smooth voice from the training room’s east entrance. Jace’s head snapped towards the voice while Clary crumpled against him, giggling into his neck. 

“Hello, Isabelle,” Jace called, slipping his hands from Clary’s pants to wave his middle finger towards the moody brunette. 

“Some people come here to train,” she accused, an all too familiar edge to her voice. Ever since Simon went off to the Academy and told Isabelle, after an embarrassing public display, that he didn't know how to be _her_ Simon, Izzy was constantly on edge, eager to pick a fight. Clary understood better than anyone how badly it hurt to have Simon’s memories repressed, yet Isabelle rarely confided in her. 

Clary regretfully removed herself from Jace and hopped down from the platform they fought on to walk towards Izzy. “Wanna talk?” Clary asked and Isabelle scoffed, rolling her eyes. 

“No. I want to fuck someone up.”

“Maybe you should just _fuck_ someone, Iz,” Clary said, shrugging. 

“Right, and who do you suppose I fuck? You and loverboy?” 

Clary looked surprised, like she had never stopped to consider this possibility. Obviously Isabelle was… _perfect_ … but Clary had never thought about sleeping with her. She hadn't really thought about sleeping with any girls, though the thought didn't gross her out. If she wasn't already so turned on maybe it would have, but she was and so it didn't. Clary realized she was staring. She closed her jaw with a snap and cleared her throat. 

“Maybe?” Clary answered finally, looking astonished. “But you've always had so many guys falling over you, it's not like it's hard for you to find someone. We could go to Pandemonium?” 

Isabelle’s eyes hardened. “No,” she said and turned towards the corner of the room where throwing knives sat on a table. 

“Wait, Isabelle!” Clary said, following after her. It was a big room and Clary wondered whether Jace had heard their conversation; when she turned around, he was no longer there and Clary sighed, jogging over to her friend. “Do you actually want to? I mean, to have sex with us?”

“Clary,” Isabelle said, her voice irritated and condescending, “I don't know what the fuck I want, okay? I want Simon back, _my_ Simon. But that's not happening and I’m just…” She huffed out a breath and grabbed a knife, throwing it perfectly at the bullseye. 

“I wouldn't be totally opposed, you know,” Clary said, picking up a knife from the table. She wasn't as good of a throw as Isabelle, though Clary assumed this would probably give Izzy a smug sense of satisfaction. She threw the knife, which hit the outside edge of the circle. Clary sighed. 

“I'm sure Jace would. He thinks of me like a sister.”

Clary eyed Isabelle, grinning. “He thought I _was_ his sister, Iz. I'm sure he can compartmentalize. I can talk to him, if you want. We are pretty good at blowing off steam, it might help.” 

“Do whatever you want to do, Clary,” Isabelle said in a tone that told Clary their conversation was over. She nodded at Isabelle and turned to leave, heading back towards Jace’s room. 

Clary’s head was spinning. Did she really just offer her friend what she thought she had? Had Isabelle really seemed to want it? Was Jace going to kill her, or worse, feel betrayed? Clary had just invited someone into bed with them. Clary felt pretty confident that she could handle watching someone play with Jace, but how would Jace feel?

She opened Jace’s bedroom door and felt the familiar humidity of shower steam filling the room. The air smelled of Jace’s spicy body wash that made Clary’s heart rate increase. She crossed the room to the bathroom and started stripping off her training gear, losing her balance as she pulled off her boot, banging into the wall slightly. 

Jace slid the shower curtain aside and grinned at Clary, arching a brow. She was only in a lacy black bra and boyshorts, her pants stuck halfway down her legs as she leaned against the wall, unlacing her boot. “So clumsy,” Jace chided with a shake of his head before closing the curtain again. 

Clary rolled her eyes and continued stripping out of her gear, joining Jace in the shower when she was unclothed. He wasted no time before cupping Clary’s face, bringing his head down to kiss her. Clary relaxed against his kiss, pulling her body flush against his. He was already hard and Clary assumed he enjoyed her half-dressed clumsiness more than he let on. 

“Jace,” Clary said, putting her hand against his chest to push him back. “Did you hear what Isabelle was saying?” 

“Nah, I figured she needed some privacy-slash-girl talk so I left pretty quickly. Plus I had a small _situation_ I had to hide,” Jace said, smiling wickedly. 

“It's hardly small,” Clary said quickly, then blushed. “Actually, it’s kind of about that.” Jace eyed Clary curiously. 

Clary grabbed for a washcloth so she didn't have to stand still in front of him while confessing. “It's just… I think Isabelle wants to sleep with us. Actually, I kind of said yes, I think?” It was all out in a single breath and Clary felt her face burning as she averted her eyes. 

Jace bent down to catch Clary’s averted eyes, and as he stood up straight again, her eyes followed his. He looked… amused. That was a good sign, right?

“What?” Jace asked, shaking his head. He was laughing and Clary was mostly sure he was laughing at her bashfulness. “Okay, wait, I need more details here.”

Clary sighed, thankful he didn't seem angry. “Well,” Clary started, her eyes wide. “She said she wanted to fuck somebody up so I was like _well, why don't you just fuck somebody instead?_ and then she was like _who am I gonna fuck, you guys?_ and I was like… maybe? I think she needs to just be distracted or something, so I was like _well, we are pretty good at blowing off steam_ and she's like _you should probably talk to Jace_ so... here I am.”

Jace brushed his wet hair off his face, looking at Clary like she was insane. “Have you thought about this before?” He looked deeply amused. 

“No,” Clary snapped, crossing her arms over her chest. “I mean, not Isabelle exactly but I’ve sort of wondered what it would be like. Have _you?_ ”

“She's like my sister,” Jace said defensively. 

“Jace,” Clary said, running a finger down his chest. “You thought I actually was your full blooded sister and that didn't stop you from wanting me.” 

Her finger drew lower until it traced the length of Jace’s hard cock. He groaned and leaned into her. “You make a valid point,” Jace said. “But I love you. I haven't even thought of anyone else.”

“Okay,” Clary said, smiling up at him. “I just had to tell you, of course. Full disclosure and all.” 

Jace nodded, pulling Clary against his body. “So, you've been curious about girls?”


	2. Rules

"Go away," Clary mumbled against her pillow, willing the persistent knock at the door to go the hell away. While she wasn't sure of the time, Clary was mostly sure it was too early to be dragged out of bed. The groan beside her confirmed her suspicions as the pillow was pulled from under her head and thrown against the door.

"Hey!" Clary protested as her head hit the mattress. "I was using that."

The groggy bear of a boy next to her growled, pulling Clary against his chest, his arm acting as a makeshift pillow. "Better?"

Clary nodded, burrowing deeper into Jace's arms. He was so warm, wrapped pliantly around her, that Clary slipped easily back into the dark grasp of sleep. That is, she dozed for mere seconds before she heard the knocking continue.

"Make it stop," Clary whined, pulling the white duvet over her head. Jace groaned as he slipped out from under Clary and went to his dresser to pull carefully-folded pajama bottoms from the middle drawer. He yawned, stumbling a little as he pulled the plaid pants on while walking to his bedroom door.

It was Isabelle. She didn't bother with hellos as she pushed into Jace's room, looking for Clary.

"Wake up," Isabelle demanded, climbing onto Jace's side of the bed. "I need to talk to you."

"No," Clary muttered, pulling Jace's pillow over her head. It smelled like him and made Clary moan slightly. "Too early."

"It is _not_ too early," Isabelle insisted, removing the pillow and pulling the covers off of Clary's head. The duvet fell down further than expected and Isabelle groaned, seeing more than she'd expected. "Clothes are a thing, you know."

At this, Clary opened one eye, somehow managing to glare through it. " _You_ came in _here_ , you can't dictate my level of dress in private quarters. What time is it, anyway?"

"That's beside the point. Up. Don't make me pull the blankets off entirely."

Jace shut the bedroom door, rolling his eyes. "You stole my spot," he said, squeezing in beside Clary on her side of the bed. "There will be consequences."

Isabelle huffed in annoyance as Jace wrapped himself around Clary. She briefly wondered where his hands were, realizing they must be somewhere on his naked girlfriend. Clary confirmed as much when she giggled.

"It seems I'm the only one who cares about sleep," Clary said, pushing Jace's hands off of her. "What time is it?"

"I don't know," Isabelle said, "Nine or something. Really Clary, I need to talk to you."

"I told Jace," said Clary with a yawn. "So if it's about that, just talk. I'll try to listen. Wait, you said it's nine? What the hell?"

"You sure didn't waste any time, did you?" Isabelle asked, a certain edge to her voice.

Jace mumbled something and Clary was giggling again, her body moving underneath the covers. If looks could kill, Clary was certain she'd be dead as she pulled the blankets off of her face and caught Isabelle's eye assessing the couple in bed. She quickly covered her head again. " _What_? You told me to talk to him so I did. You can't be annoyed at me when you barge in her at the crack of dawn. Why aren't you sleeping?"

"Because I _can't_ sleep," Isabelle hissed. "Forget it. Come find me when you're decent." She stormed out of the room, yanking the door open and slamming it behind her as her heels clicked down the hallway.

Jace pulled the covers off of their heads, grinning at Clary. "She really does need to blow off some steam," he noted, a hint of something in his voice.

"I need to blow off _something_ after that encounter," Clary agreed as Jace climbed over her to his side of the bed. As if her words suddenly registered in his sleepy mind, Jace turned over in bed, looking sharply at Clary.

"Oh?" he asked, quirking a perfect blond brow.

Clary nodded devilishly as she threw the covers over her head and scooted down towards the foot of the bed, dragging Jace's pajamas down with her.

*

It was an hour later when Clary rolled out of bed, leaving a sleeping Jace in her wake. She was too awake to fall back to sleep and cursed Isabelle under her breath as she pulled out some clothes. As far as compatibility went, Clary was constantly amazed at how well she and Jace worked together despite their completely opposite natures. She was forever leaving her drawer an absolute mess, yet every time she opened it, Jace appeared to have put it all back together, folding her clothes neatly into piles. It tugged at Clary's heart as she grabbed an outfit, and if she were being completely honest, she often left the drawer a mess just so she could smile at the way Jace reorganized it.

After throwing on her sweater and leggings, brushing her teeth, and throwing her wild hair into a messy bun, Clary headed out into the Institute in search of Isabelle. The scent of freshly brewed coffee led Clary into the kitchen where Isabelle sat at a bar stool, looking accusingly at her mug of coffee.

"Morning," Clary said, heading to the coffee maker. She stopped at the machine, then turned slowly towards Isabelle. "Did you… make this?" Clary asked, side-eyeing the coffee pot.

"It's only _coffee_ ," Isabelle said moodily; Isabelle was notoriously dangerous in the kitchen and was rarely trusted to produce anything even remotely edible.

"Is there anything more important than a properly-made cup of coffee?" Clary asked, reaching for a mug hesitatingly. "Bach said 'without my morning coffee, I'm just like a dried up piece of roast goat.' By that logic, there is no such thing as _only coffee_."

Isabelle rolled her eyes hard enough that Clary swore she could actually hear it. Not wanting to mess with her fate any further, Clary filled her mug with coffee that smelled suspiciously bitter and lugged it to the counter next to Isabelle.

"So, want to talk?"

Isabelle turned her head slightly so that she could glare at Clary. "No. Yes. I don't know." Her head fell into her hands and she sighed. Clary looked over at Isabelle, noticing the way her voyance rune moved over her bony hand. "What did Jace say?"

"Well, nothing much. We got… distracted." Clary said this last word as gently as possible, hoping it wasn't received as strongly as it felt leaving her lips. "He didn't say no, though." Clary suddenly felt like she was saying something dangerous so she lifted the coffee to her mouth, wincing slightly at the taste. "Maybe we could all talk about it?"

Isabelle sighed, sitting up slightly to brush her long, dark hair out of her face. "This is weird," Isabelle said, making a face.

"The coffee?" Clary asked, then quickly corrected herself upon seeing Isabelle's reaction. "I mean, the coffee is great. The other thing is weird, then?"

Isabelle nodded, looking glum. "It's a stupid idea."

"Yeah, totally," Clary agreed quickly. Then she met the taller girl's eye and grinned. "But it could be fun?"

"Why would you want to? You guys are like, disgustingly in love with each other. It will be weird."

"We don't have to do it, Iz. It just came up, heat of the moment kind of thing. If you don't want to-"

"I do want to," Isabelle said, cutting Clary off. Clary was honestly unaware that Isabelle had it in her to look shy but it was definitely there on her face. "I don't know why but it could be fun. A good distraction. Blowing off steam or whatever you said last night."

"Right," Clary agreed, taking another sip of her coffee. "Hey, Izzy, have you ever… you know, slept with a girl?"

Izzy grinned and that was all it took for her to look like herself again, daring, bold Isabelle. "Do you really think there's anything I haven't tried?" Clary shrugged, as if to say _probably not_ and Isabelle laughed. "I'm guessing you haven't?"

"Correct." Clary was finding it suddenly difficult to look at Isabelle and she suspected Isabelle knew it.

As if to save her, or to perhaps make matters worse, Jace entered the kitchen, rubbing sleep from his eyes. He was still only wearing pajama pants and Clary's eyes went instinctively to his broad chest. When she looked up, Jace was grinning at her.

"Like what you see?" he asked, heading to the coffee maker. He assessed the pot, then looked towards the girls. "Who made this?"

Isabelle sighed exasperatedly, throwing her hands up in defeat. "It's _coffee_!" she insisted. "By the Angel, you'd think it was ichor!"

Jace looked back towards the pot, as if wondering whether he'd actually rather drink ichor. He yawned and it seemed to convince him that he'd probably drink ichor as long as it was in fact caffeinated. He grabbed a mug from the cabinet and filled it before walking towards the place the girls sat at the counter. There were only two stools so Jace hopped up on the counter top, taking a sip of coffee; he made sure he didn't wince.

"So," Jace said, feeling the tension in the room. "What are we talking about?"

"The whole having-sex thing," Isabelle responded casually, causing Clary to choke on her coffee. Both Jace and Isabelle looked at Clary whose cheeks suddenly burned. Jace loved it when she blushed.

"Perfect conversation this early in the morning," Jace asserted, looking between the two girls. _They really could not be less alike_ , Jace thought in amusement. Isabelle was so tall, nearly as tall as Jace, with long, stick straight and sleek dark hair, nearly as dark as night. Her eyes were dark, too, and the combination was bright against her pale olive skin. And then there was Clary, Clary Fairchild, whose named suited her well. She was all color while Isabelle was so black and white, her eyes a deep green, her hair bright red and curly. Light brown freckles dusted her nose and cheeks, which were frequently rosy whether by embarrassment or exertion.

Then there was the matter of their personalities. Both of them were strong young women, fierce and powerful, but the way they carried their power was so different. Clary was modest, shy, and prone to outbursts of passion while Isabelle was confident, sexy, and significantly more moody than Clary. It was somewhat interesting, really, how different the two of them were.

"So, are we all in?" Jace asked, eyeing the girls. They each nodded, Clary looking bashful and Isabelle wearing a more annoyed defeat. "Should we talk about, like, rules? Boundaries? I don't know, I've never really orchestrated anything like this."

Isabelle snorted, burying her face in her hands. "This is ridiculous," she said, shaking her head.

"What kind of rules?" Clary asked, reaching up to adjust her messy bun.

"Well, I want to be drunk. That's rule one." Jace said casually.

"Seconded," Izzy said.

"Yeah, same," echoed Clary.

"So, we can go to Pandemonium? Get drunk? Come back and then-?"

"Proceed accordingly," Isabelle suggested, sighing. "I have a rule, though. Nobody knows. Nobody. Not Alec or Magnus and especially not Simon."

"Do you think Simon would be upset?" Clary asked, glancing at Isabelle hesitantly.

" _Simon_ has decided he doesn't want me, so no. I'd just prefer to not broadcast this," Isabelle responded bitterly.

"So: drunk, and nobody knows," Jace said. "Any more rules?"

"I'd prefer condoms be used between you guys," Clary said sheepishly. "No offense, Iz, I know you use the birth control rune, it's just…"

"Intimate. I get it," Isabelle said cooly. "God, this is weird."

Clary and Jace nodded in unison, sharing a glance between them. _I trust you_ , it said. _I love you. You are mine._ Clary smiled and Jace returned the sentiment. _This could be fun._

"No weapons," said Isabelle, glaring at Clary. "I saw you guys in the practice room."

Clary laughed and covered her eyes, licking her lips subconsciously as if remembering the taste of Jace's blood. "Drunk, nobody knows, condoms, no weapons. Though, Isabelle, that was… not how we usually do things, for the record."

Isabelle shrugged. "That's your business."

Jace laughed into his coffee mug and Isabelle noticed the way his stomach muscles flexed, averting her eyes quickly. She wasn't used to letting herself notice this stuff about Jace. There may have been a time when Isabelle wondered what it would be like to touch him but it was buried years ago. She nearly felt nervous at the idea of finding out.

"I don't want to use my room," Jace said, setting down his empty mug. "Too personal."

The girls nodded in agreement. "There are tons of rooms in this place," Clary said, gesturing out of the kitchen. "I don't think finding a secluded one will be a problem, then we don't have to use any of our rooms."

"I don't want to hear you guys professing your love to each other, if that's not too much to ask," Isabelle said. "The whole third wheel thing is weird enough just living with you."

Clary rolled her eyes, but she was smiling despite it. "Drunk, nobody knows, condoms, no weapons, spare room, no declarations of love. Got it. Is that all?"

The three friends looked around at one another, somewhat wearily but with a certain undertone of excitement, like children plotting to spoil their Christmas surprises. But it isn't like that, Isabelle reminded herself; I'm just trying to forget for a while, not spoil anything.

"Are you sure you guys are okay with this?" Isabelle asked, looking questioningly between Clary and Jace.

The couple looked between each other again, sharing more wordless affirmations. _It's just sex. I'll always love only you. It'll be fun. She needs some fun._ They turned back to Isabelle, both of them nodding.

"I'm more worried about the me part than the you part," Clary said, gesturing between Jace and Isabelle. "I've never… done anything like this."

Isabelle smiled, the kind of smile that did more to intimidate than comfort. Clary gulped. "I'll show you a good time if you make my brain stop working for a while."

Clary raised an eyebrow and then held out her hand for Isabelle to shake. "Deal."

**Notes for the Chapter:**

> Welp, so here goes nothing! Next up... sex.


End file.
